Newcastle Disease in Chickens: Symptoms, Causes and Treatment

Newcastle Disease is caused by Newcastle Disease Virus (NDV), classified by pathogenicity into three groups that produce very different clinical pictures.

• Lentogenic (low virulence) NDV: Causes only mild respiratory signs or subclinical infection. Most commercial vaccines use lentogenic strains (La Sota, B1). Wild bird contact commonly introduces lentogenic strains into backyard flocks.
• Mesogenic (medium virulence) NDV: Causes respiratory and nervous system signs with moderate mortality. Rare in the US due to regulatory control; historically important in commercial flocks.
• Velogenic (high virulence) NDV: The form that causes the reportable disease known as Virulent Newcastle Disease (vND). Two subtypes exist: viscerotropic (GI tract hemorrhage, high mortality) and neurotropic (nervous system damage, high mortality). The 2018-2022 vND outbreak in California affected over 400 flocks.
• Transmission: NDV spreads through direct contact with infected birds, contaminated feces, secretions, feathers, and surfaces. Wild birds (especially cormorants and shorebirds) are a major natural reservoir. The virus survives on equipment and clothing for days.
• Zoonotic potential: NDV can cause mild conjunctivitis and flu-like symptoms in humans who handle infected birds without eye protection. It does not spread person to person and is not a significant human health threat.

Newcastle Disease must be distinguished from other respiratory and neurological diseases. The combination of rapid flock spread, respiratory signs, AND neurological signs together is highly suspicious for velogenic NDV:

• Clinical pattern: Rapid onset (hours to days), affecting most of the flock simultaneously, with both respiratory and neurological signs, is the hallmark of velogenic NDV. Other respiratory diseases do not typically cause neurological signs.
• Differential diagnoses: Infectious Bronchitis (respiratory only, no neuro), Marek's Disease (neuro only, slower onset), Avian Encephalomyelitis (neuro, mainly young birds), and Egg Drop Syndrome (reproductive only).
• Do not wait for laboratory results: If velogenic NDV is suspected, immediately contact your state veterinarian. Do not submit samples through normal channels. USDA APHIS has a national NDV hotline and will direct sample submission and response.
• Laboratory confirmation: PCR, virus isolation, and hemagglutination inhibition testing confirm diagnosis and pathotype at USDA National Veterinary Services Laboratories (NVSL).

There is no antiviral treatment for Newcastle Disease. Management depends on pathotype severity.

Lentogenic NDV: Supportive care, electrolytes, and monitoring. Vaccinate unaffected birds on the property with a Newcastle-approved live vaccine (La Sota or B1 strain via drinking water or eye drop). Improves recovery time and reduces mortality.

Mesogenic or velogenic NDV (reportable): USDA APHIS takes over management. Infected premises are quarantined. Affected birds are depopulated (culled) to stop spread. Movement of all poultry, poultry products, and equipment from the premises is prohibited. Indemnification payments are available for commercial operations under federal law.

Vaccination for prevention: Newcastle vaccines (La Sota, B1, Clone 30) are available as live attenuated vaccines for water, spray, or eye-drop administration and as killed oil-adjuvant vaccines for boosters. Consult a veterinarian for the appropriate regimen based on regional risk.

• Vaccinate against Newcastle Disease with a La Sota or B1 strain vaccine at 1-2 weeks of age (eye drop or water), boost at 4-6 weeks, and revaccinate every 6-12 months based on risk. Vaccination is the single most important preventive measure.
• Practice strict biosecurity. Dedicate boots and clothing to poultry areas. Visitors from other farms are the most common source of introduction after wild bird contact.
• Minimize contact with wild birds. Net overhead runs, reduce standing water that attracts waterfowl, and do not feed wild birds near poultry areas.
• Quarantine all new birds for 30 days before flock integration. NDV can be shed by clinically normal vaccinated carriers during incubation.
• Know your reporting obligation. In the US, velogenic NDV is a federal and state listed disease. Suspicion alone -- not laboratory confirmation -- triggers the mandatory reporting requirement.